The bacteria that make work easier for crime scene investigators everywhere

Thanks to the modern TV viewer’s enthusiasm for zombies, plus the everlasting appeal of crime procedurals, there’s no shortage of conversation about dead bodies in popular culture. Medical examiners and forensic investigators on shows like CSI, Bones and Law & Order: SVU have routine, casual conversations about murder victims in various stages of decomposition, and the very premise of The Walking Dead is based on undead, rotting corpses walking around and terrorizing people.

Despite this, well, appetite for what happens to a body after death, scientists are still learning about the biological processes that go on during decomposition, including the activity of the various bacteria, fungi and tiny scavengers that make quick work of corpses. A study published today in Science, led by Rob Knight from the University of California San Diego, looks at the microbes that contribute to decomposition, and shows that they are surprisingly similar in both human bodies and mice, in different types of soil and during different seasons, both indoors and out.

Jack Gilbert, PhD

Jack Gilbert, PhD, and his team at the University of Chicago and Argonne National Laboratory collaborated on the analysis and interpretation of the study. “This study is the first to demonstrate the metabolic opportunists that lurk in every soil, and perhaps every environment, on earth. When a dead animal hits the ground there are bacteria and fungi that migrate to the body, but that appear to be potentially found everywhere on earth,” Gilbert said. “This means that bacteria have evolved patience, and the capacity to respond to this food source when it happens to land on their plate!”

Fortunately, the researchers didn’t have to recruit actual zombies to gather their data. The human experiments took place at the Sam Houston State University Southeast Texas Applied Forensic Science Facility, a two-acre, fenced-in area located a few miles north of Huntsville, Texas. Knight’s team placed two cadavers—generously donated for scientific research—outside in February, and took several samples a week from the bodies and surrounding soil until April. They placed two more cadavers outside again later in April, taking samples through July. The team performed similar experiments with mice in a laboratory at the University of Colorado.

After analyzing the samples, they saw that the community of microbes hanging around during decomposition developed in a similar pattern, regardless of the type of environment or season, human or mouse.

Knowing that microbes congregate in such a predictable way will help scientists studying ecosystems like forests get a better understanding of how mammal deaths contribute to organic matter and food sources. It could also provide more data during death investigations to determine time and place of death, based on which microbes are present. So if you start hearing CSI techs throwing around names of microbial species like Bifidobacteriales and Discicristata on your favorite TV series, you’ll know it’s based on real science.